The grounds for this invention are the sealing problems that relate to valve spindles. Rotatable as well as axially movable valve spindles are in practice often sealed by gland or radial sealings. These sealings include a set of rings that via a washer and a number of screws are compressed axially in order to expand radially and thus create a sealing between the spindle and a surrounding valve housing. However, the sealing is worn and consequently the sealing pressure decreases eventually. A regular follow-up draft of the screws is thus required. Sometimes spring washers beneath the heads of the screws are used to give a more long-lasting axial prestressing of the set of rings. For certain types of valves O-ring sealings are also used. These sealings have the disadvantage that the valve must be dismounted when the O-ring is to be exchanged.
Common for prior art valve sealings is that a relative movement takes place in the interface between the sealing material and the spindle. This means that the sealing will never become hermetically tight in absolute terms and as soon as the sealing is worn its sealing ability is reduced gradually. In e.g. the process industry, like chemical industry, there are very high demands upon valve tightness since fluids, whose flows are regulated by means of a valve, may be toxic as well as corrosive. A leaking gas valve, e.g. at an oil rig, may cause catastrophes.
Hermetically tight valves that use metal bellows are known for such valves where the valve operation is effected by an axial movement only, e.g. sliding valves and seat valves. In such a case the valve spindle at its outer end is provided with a thread that cooperates with a journalled nut that upon rotation causes the spindle to move axially. Inside of the thread and the nut a metal bellows is provided and it is possible to secure said metal bellows both to the spindle and the surrounding valve housing in a hermetically tight way due to the fact that the spindle moves only axially, i.e. without rotating. For other types of valves, e.g. ball valves, cap valves and revolving butterfly valves, it is necessary when operating said valves that the spindle is rotated or turned. This makes it impossible to secure a bellows hermetically tight to the spindle. The operation of said valves often requires that high torques are transmitted from the driving source in question to the rotatable spindle and the adherent valve body.
From a narrow aspect the aim of the invention is to realize a device that manages to transmit also high torques to a rotatable valve spindle simultaneously as the spindle is kept separated from the surroundings by means of a separating means that is hermetically tight. From a most general aspect the aim of the invention is to create a device for transmitting a torque that could be used wherever a rotational element is to transmit a torque to another rotational element simultaneously as the elements are kept apart by means of a hermetically tight separating means.
A device as generally defined in the preamble for transmitting a rotary motion is previously known for other purposes than operation of valve spindles. This known device has two rotational elements that consist of input and output shafts that are rotatably journalled in opposite walls of a housing that is placed in a partition between two separated spaces. The transmission element consists of a rigid arm that is pivotally journalled by means of a ball and socket joint located between the ends of the arm, the opposite ends of the arm being hingedly connected with discs on the input and output shafts respectively; more precisely in such a way that the arm transmits a rotary motion with a gear change of 1:1 from the input shaft to the output shaft. The arm is provided with a plate to which an end of a conically shaped bellows is tightly secured, the opposite end of the bellows also being tightly secured to one of said walls in the housing.
For several reasons it is not in practice possible to use a device of the last-mentioned type for transmitting high torques between input and output rotational elements, e.g. in a valve, simultaneously as hermetical sealing is guaranteed. Thus the bellows is moving with large strokes; this means that the bellows must not be made out of materials, e.g. metallic materials, that are resistant to high pressures. Further the arm that takes care of the transmission of rotation of the input shaft to the output shaft has such weak dimensions that it is not at all possible to transmit higher torques. Still further the structure does not allow fine adjustment of the output rotational element in different setting positions.